Traditional high temperature devices are generally placed several distances from high temperature environments in order to prevent them from failing, due to the inability to survive the high temperature. Generally, the failure of these devices (e.g., sensors and electronics) is due to the instability or lack of robustness of the contact metallization and packaging. Unique problem characteristics are the effects posed by temperature on semiconductor sensors and electronics as they are further inserted into the higher temperature sections of the monitored environment. This is primarily because, as the devices with traditional electrical ohmic contacts are inserted further into higher temperature sections, their performance characteristics degrade dramatically to the point that they fail catastrophically.
As a result of the aforementioned scenario, devices with conventional ohmic contact metallization are generally placed several distances away from environments having extreme temperatures. In other words, the devices are positioned in lower temperature sections (e.g., of an engine) where the temperature would not adversely impact the contact metallization or the package.
In addition to the above disadvantage of conventional metallization on devices, there is also a problem of complexity and production costs that is associated with their fabrication. Most semiconductor electronic and some sensing devices operate in bi-polar mode, which means that the device's physical configuration contains sections that are doped either n- or p-type. As a result, the metallization needed to make ohmic contact to either of the layers is exclusive to that layer. This means that below a certain doping level, a metal (or metal compound/mixture) that is ohmic on an n-doped layer generally would be rectifying on a p-doped layer. Conversely, a metallization that is ohmic on a p-doped layer would be rectifying if deposited on an n-doped layer.
Therefore, on a bi-polar device, multiple process steps of successive depositions, photolithography, and etchings are required to deposit and pattern the desired ohmic contact metallization. This process is time consuming and expensive. For example, in some instances, one of the layers is degenerately doped (usually the p-type SiC) so that the exclusivity is removed, thereby making it possible for a single metal to be ohmic on both n- and p-type layers. The process of forming a degenerately doped layer in the contact area is by high-energy ion implantation. This entails surface preparation prior to ion implantation, usually performed at temperatures around 1100° C. As can be appreciated, the process not only adds cost, but the implantation process itself causes damage to the lattice structure of the device. The induced damage can only be partially reversed after annealing. Post ion implantation also requires that the implant be activated at temperature as high as 1200° C., and it is known that not all the implants are fully activated.